Power-series convergence and differentiation
For Σaₙ(x−c)ⁿ the radius R is 1/lim sup|aₙ|¹⁄ⁿ, with 1/0=∞ and 1/∞=0.
Key knowledge
For Σaₙ(x−c)ⁿ the radius R is 1/lim sup|aₙ|¹⁄ⁿ, with 1/0=∞ and 1/∞=0. Inside R the sum converges absolutely, uniformly on smaller closed intervals, and can be differentiated term by term; the derivative has the same radius.
Conditions and scope
- Endpoint convergence is checked separately.
- Smooth real functions need not equal their Taylor series.
Sources · 1
References
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Evidence and review
Theorems 10.3, 10.6 and 10.20–10.22; smooth/nonanalytic distinction in section 10.7.
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Entry details
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